Fasting heat production of Saanen and Anglo Nubian goats measured using open-circuit facemask respirometry.

This study aimed to establish the heat production (HP) of Saanen and Anglo Nubian goats at absorptive (feeding) and at post-absorptive (fasting) statuses to determine the adequate period of fasting required for the measurement of basal metabolism. Gas exchange was recorded via open-circuit facemask respirometry. Six non-lactating and non-pregnant goats of each breed, Saanen (49.2 ± 3.2 kg of body weight, BW) and Anglo Nubian (64.0 ± 3.0 kg BW), were placed in individual pens with ad libitum access to the same total mixed ration. After a 3-day feeding period, the animals were subjected to fasting (no feed), and the gas exchange measurement was performed for 30 min at 0, 12, 20, 36, 44, 60 and 68 h after fasting. The daily HP of the Saanen and Anglo Nubian goats averaged 557.4 ± 38.7 and 357.1 ± 35.3 kJ/kg0.75  BW day respectively. During fasting, the methane production decreased exponentially in both breeds, and the critical time when methane production was statistically equal to zero was at 31 h of fasting for the Saanen goats and at 40 h for the Anglo Nubian goats. The daily HP and respiratory exchange rate during fasting decreased up to 60 h. Taken together, our results suggest that the ideal period to measure fasting heat production (FHP) for goats fed at maintenance levels should be between 40 h and 60 h of fasting. Consequently, the daily FHP, after 60 h of fasting, of Saanen and Anglo Nubian goats was 183.3 ± 16.3 and 211.1 ± 11.5 kJ/kg0.75  BW day respectively. The results presented herein are relevant for future studies of energy metabolism in goats.

Net macromineral requirements in male and female Saanen goats.

These experiments estimated Ca, P, Mg, K, and Na requirements of intact male, castrated male, and female Saanen goats. Two experiments were performed: one to determine the net macromineral requirements for maintenance (Exp. 1) and another to determine net macromineral requirements for growth (Exp. 2). In Exp. 1, 75 goats (26 intact males, 25 castrated males, and 24 females) with initial BW (iBW) of 15.76 ± 0.10 kg were used. These animals were divided in 2 groups: baseline animals and pair-fed animals. Twenty-one goats (8 intact males, 7 castrated males, and 6 females) were slaughtered (16.6 ± 0.96 kg BW) at the beginning of the experiment to be used as the baseline group. The 54 remaining goats (18 intact males, 18 castrated males, and 18 females) were pair fed in 6 blocks of 3 goats per sex. The goats within each block were then randomly allocated to 1 of 3 levels of intake: ad libitum, restricted fed to 75% of the ad libitum intake, and restricted fed to 50% of ad libitum intake. When the animal fed ad libitum reached 31.2 ± 0.58 kg BW, it and the other goats from the same block were slaughtered. The effects of sex and level of intake were evaluated in a split-plot design, where sex was the main plot observation and level of intake was the subplot. Daily net macromineral requirements for maintenance did not differ among the sexes ( > 0.05), and the average values obtained were 35.4 mg Ca, 24.7 mg P, 2.5 mg Mg, 5.0 mg K, and 3.30 mg Na per kg BW∙d. The net requirements for growth in Exp. 2 were obtained using 58 goats (20 intact males, 20 castrated males, and 18 females) with 15.8 ± 0.11 kg iBW, all fed ad libitum. These animals were assigned in a completely randomized design and allocated in 3 slaughter weight groups: 16.6 ± 0.96, 23.1 ± 1.33, and 31.2 ± 0.58 kg BW. The net Ca, P, and Mg requirements for growth were not different among the sexes ( > 0.05). There was a sex effect on net K and Na requirements for growth ( < 0.05). The net K requirements for growth (g/kg ADG) of intact males were greater ( = 0.03) and increased approximately 16%, whereas females and castrated males decreased approximately 11% as BW increased from 15 to 30 kg BW. The net Na requirements for growth (g/kg ADG) increased 9.5% for intact males and decreased 22% for females when the goats grew from 15 to 30 kg BW. Sex, therefore, affects net K and Na requirements for growth, but it does not affect net macromineral requirements for maintenance in Saanen goats.

Energy requirements for growth in male and female Saanen goats.

The aim of this study was to investigate the energy requirements of female and intact and castrated male Saanen goats. Animals were randomly assigned to 1 of 2 experiments designed to investigate the energy requirements for maintenance and gain. To determine the maintenance requirements, 85 goats were used (26 intact males, 30 castrated males, and 29 females) with an initial BW of 30.3 ± 0.87 kg. Thirty goats (8 intact males, 9 castrated males, and 13 females) were slaughtered to be used as the baseline group. The remaining goats were assigned in a split-plot design using a 3 × 3 factorial arrangement (3 sexes-intact males, castrated males, and females-and 3 DMI levels-ad libitum and restricted fed to 75 or 50% of the ad libitum intake). The NE was obtained using 65 goats (20 intact males, 22 castrated males, and 23 females) fed ad libitum in a completely randomized design. Eight intact males, 9 castrated males, and 13 females were slaughtered at 30.5 ± 1.53 kg BW. Seventeen goats (6 intact males, 6 castrated males, and 5 females) were slaughtered at 38.1 ± 0.49 kg BW. The remaining goats were slaughtered at 44.0 ± 0.50 kg BW. The NE did not differ between the sexes ( = 0.59; 258.5 kJ/kg BW), resulting in a ME for maintenance of 412.4 kJ/kg BW. The estimated energy use efficiency for maintenance was 0.627. During the growth phase, NE differed between the sexes ( < 0.001); intact males, castrated males, and females showed an average NE equal to 15.2, 18.6, and 22.7 MJ/kg of empty weight gain, respectively. The energy requirements for growth differed between the sexes. The difference was found to be due to distinct NE and partial efficiency of ME utilization for growth in intact and castrated males and females during the late growth phase. This study may contribute to adjustments in feeding system energy recommendations regarding the NE and NE found for goats during the late growth phase.